The advent of digital cinema has created new standards for cinema sound, such as the incorporation of multiple channels of audio to allow for greater creativity for content creators and a more enveloping and realistic auditory experience for audiences. Model-based audio descriptions have been developed to extend beyond traditional speaker feeds and channel-based audio as a means for distributing spatial audio content and rendering in different playback configurations. The playback of sound in true three-dimensional (3D) or virtual 3D environments has become an area of increased research and development. The spatial presentation of sound utilizes audio objects, which are audio signals with associated parametric source descriptions of apparent source position (e.g., 3D coordinates), apparent source width, and other parameters. Object-based audio may be used for many multimedia applications, such as digital movies, video games, simulators, and is of particular importance in a home environment where the number of speakers and their placement is generally limited or constrained by the confines of a relatively small listening environment.
Various technologies have been developed to more accurately capture and reproduce the creator's artistic intent for a sound track in both full cinema environments and smaller scale home environments. A next generation spatial audio (also referred to as “adaptive audio”) format, and embodied in the Dolby® Atmos® system, has been developed that comprises a mix of audio objects and traditional channel-based speaker feeds along with positional metadata for the audio objects. In a spatial audio decoder, the channels are sent directly to their associated speakers or down-mixed to an existing speaker set, and audio objects are rendered by the decoder in a flexible manner. The parametric source description associated with each object, such as a positional trajectory in 3D space, is taken as an input along with the number and position of speakers connected to the decoder. The renderer utilizes certain algorithms to distribute the audio associated with each object across the attached set of speakers. The authored spatial intent of each object is thus optimally presented over the specific speaker configuration that is present in the listening environment.
Current spatial audio systems provide unprecedented levels of audience immersion and the highest precision of audio location and motion. However, since they have generally been developed for cinema use, they involve deployment in large rooms and the use of relatively expensive equipment, including arrays of multiple speakers distributed around a theater. An increasing amount of advanced audio content, however, is being made available for playback in the home environment through streaming technology and advanced media technology, such as Blu-ray disks, and so on. For optimal playback of spatial audio (e.g., Dolby Atmos) content, the home listening environment should include speakers that can replicate audio meant to originate above the listener in three-dimensional space. To achieve this, consumers can mount additional speakers on the ceiling in recommended positions above the traditional two-dimensional surround system, and some home theater enthusiasts are likely to embrace this approach. For many consumers, however, such height speakers may not be affordable or may pose installation difficulties. In this case, the height information is lost if overhead sound objects are played only through floor or wall-mounted speakers.
To facilitate the playback of adaptive audio content in home environments, efforts have been made to replace height or ceiling speakers with speakers oriented upwards to reflect sound off a surface (typically the ceiling) such that sounds intended to originate from the height location do so through reflections bounced off of the ceiling. To provide accurate sound rendering, such speaker systems must provide some sort of filtering to compensate for the direct and reflected sound components played through the same speaker. Current solutions provide circuits that electrically or digitally filter the signal transmitted to the speaker, where the filter compensates for height cues in sound waves which travel directly through the listening environment to the listener in favor of height cues present in the sound reflected off the surface. Such as filter may be referred to generally as a “pinna filter.” A practical electrical implementation of the pinna filter typically requires a significant number of electrical components, such as capacitors, inductors and resistors. Depending on filter and speaker design, the cost of these components can be more than the cost of the loudspeaker driver itself. Moreover, a digital filter implementation of the pinna filter is not always feasible and depends on the capabilities of the rendering system or home theatre system. Other solutions that have been developed include modifying the speaker driver itself to have a frequency response that is close to the desired pinna filter response.
What is needed, therefore, is a speaker design that enables floor-standing and bookshelf speakers to replicate audio as if the sound source originated from the ceiling. What is further needed is a home-audio speaker system that provides fully encompassing three-dimensional audio without expensive installations or alteration of existing consumer home theater footprints.
What is further needed is a home-audio speaker system that provides appropriate pinna filter response for upward firing speakers using simple speaker components.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions. Dolby and Atmos are registered trademarks of Dolby Laboratories Licensing Corporation.